Electronic elements using carbon nanotubes have been studied intensely. A carbon nanotube has a basic structure in which a graphene sheet having a hexagonal mesh-like structure of a carbon atom is rolled to have a cylindrical shape. When carbon nanotubes are miniaturized to be single-walled carbon nanotubes (SWNT) or double-walled carbon nanotubes (DWNT), the carbon nanotubes have metallic electric characteristics or semiconducting electric characteristics depending on a difference in the diameter or chirality. The carbon nanotubes having the respective electric characteristics are expected to be used for electronic devices. Although carbon nanotubes are still in the research phase, various examples of applications of carbon nanotubes to electronic devices have been reported.
For example, WO 02/063693A1 suggests a structure of an electrode electrically connected to multi-walled carbon nanotubes. According to this structure, the carbon nanotubes are cut just before the formation of the electrode, metal that is strongly chemically-bound to a carbon atom is formed on the cut carbon nanotube to form the electrode. This reduces the contact resistance between the electrode and the carbon nanotubes in order to realize the application to an electronic device.
Japanese Patent Laid-Open Publication No. 2004-171903 suggests a field-effect transistor structured in which a metallic inner layer of double-walled carbon nanotubes functions as a gate electrode and a semiconducting outer layer functions as a channel. The Japanese Patent Laid-Open Publication No. 2004-171903 also discloses a field-effect transistor, as a prior art, in which a semiconducting inner layer of double-walled carbon nanotubes functions as a channel region and a metallic outer layer functions as a gate electrode.
As described above, the application of carbon nanotubes to electronic devices has been reported. However, only a few methods have been reported to manufacture single-walled or double-walled carbon nanotubes having a semiconducting property with superior reproducibility.
For example, Japanese Patent Laid-Open Publication No. 2004-182537 discloses the generation of a carbon nanotube having a desired diameter by forming minute projections at the surface of a silicon substrate to coat catalyst metal only on the tip ends of the projections.
Chemical Physics Letter 382 (2003)361 discloses that laser light is emitted to catalyst metal required for the formation of a carbon nanotube to gasificate the catalyst metal to fall and accumulate the gasificated catalyst metal on the substrate via gas stream to support the fine particle-like catalyst metal by the surface of the substrate. According to this method, fine particles of catalyst metal having a desired diameter can be generated. The use of such catalyst metal to grow carbon nanotubes can realize the manufacture of a carbon nanotube having a desired diameter or shell number.